The two halves of the bilayer of most biological membranes are neither structurally nor functionally symmetric. It is, therefore, anticipated that membrane bound amphiphiles, e.g. drugs, local anesthetics, etc. will partition unevenly between the outside and inside of a membrane. Since the partitioning of a drug across the membrane will influence the drug's ability to interact with membrane components which are also asymmetrically distributed, it is important to understand how certain variables, e.g., pH, the concentration of divalent cations, drug charge and concentration, etc. affect the partitioning of molecules between the two sides of a membrane. The goal of this project is to i) determine the partition coefficients of several cationic, anionic and uncharged amphiphiles between the outer and inner halves of the human erythrocyte membrane, ii) evaluate the effect of amphiphile concentration on these partition coefficients, and iii) determine the effect of two possible modifiers of drug partitioning, pH and buffered Ca++ concentration, on the transbilayer distributions of these differently charged molecules. The transbilayer distribution patterns of the various drugs/anesthetics will be evaluated by means of 19F NMR. The fluorine labeled amphiphiles to be studied include triflupromazine (an analogue of chlorpromazine), fluphenazine, trifluperidol, trifluoroprilocaine, quaternary trifluoroprilocaine, and the 5,5 gem-difluoro derivatives of n-hexan-l-oic acid, n-hexan-l-ol and n-hexyl-l-amine. The relative sizes of the internal and external populations of the membrane bound amphiphiles will be evaluated by use of impermeable NMR shift/relaxation reagents.